A circuit board includes a circuit pattern mounted on an electric insulating substrate, and is used to mount electronic parts thereon.
The electronic parts may include a heat emitting device, for example, a light emitting diode (LED), and the heat emitting device significantly emits heat. The heat emitted from the heat emitting device increases the temperature of the circuit board to cause the erroneous operation of the heat light emitting device and to degrade the reliability of the heat emitting device.
Therefore, in the circuit board, a heat radiation structure to emit heat from the electronic parts to the outside is important, and the thermal conductivity of the insulating layer formed in the circuit board exerts a great influence on the circuit board.
In order to enhance the thermal conductivity of the insulating layer, an inorganic filler must be filled in the insulating layer at a high density. To this end, epoxy resin representing low viscosity has been suggested.
As the low-viscosity epoxy resin, bisphenol A epoxy resin and bisphenol F epoxy resin are generally extensively used. Since the above epoxy resin is in a liquid phase at a room temperature, the handling of the above epoxy resin is difficult, and the above epoxy resin represents weak heat resistance, mechanical strength, and tensile force.